Volume control



Nov. 24, 1931. N. c. scHELLl-:NGER 1,833,042

VOLUME CONTROL Filed Jan. 2o, 195o 2 sheets-sheet 1 li i- Z9 304, MZ. M

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NOV- 24, 1931, N. c. SCHELLENGER 1,833,042

VOLUME CONTROL Filed Jan. 2o. 192,0 2 sheets-sheet 2' cny antenna-Nov. 24, 1931 *"NIT'ED 1 STATES PATENT oFFIcE NEWTON C. SCHELLENGER, OF FLKHART, INDIANA, ASSIGNOR '.l.0v CHICAGO TELEPHONE SUPPLY COMPANY, F ELKHART, INDIANA, A CORPORATION 0F INDIANA.`

VOLUME coNTnoL Application nleaJanuary 2o, 1930. lserrano. 422,028. y

This invention relates to volume controls, more particularly to volume controls of the tandem type and has for its principal object the production of a new and improved volume control that can be manufactured cheaply without sacrificing quality of materials n and workmanship.

1n electrical apparatussuch as radio sets, audlo frequency amphers, X-ray apparaf tus and the like, 1n which vacuum tubes are employed to amplify or generate high fre-- quency alternating current, it has become the standard practice to'control theamplitude of such alternating current by means of resistors which have therefore assumed the trade name of volume controls. In a radio set for example the loudness of the set is gen-I erally controlled by a resistor which is usually bridged across the secondary of a coupling transformervwith the.` grid `of one of the vacuum tubes connected toy the rider of the volume control.

Frequently in radio setsit is desirable to control the gain of the amplifiers at more" than one point in the' set and for this reason volume controls are frequently constructed with two or more resistors mechanically connected together to be operated bya single knob on the panell of the radio instrument. Although the resistors are n'lechanically Icon,- nected together, they are electrically insulated from each other and connected into entirelv different parts of the electrical circuit of the radio set. of the present invention 'is of this multiple unit or so-calledA tandem type, although many of the principles of its construction can be employed insingle unit resistors or v olume controls.

To this end I have provided a compact unit which can be constructed cheaply without sacrificing quality, either of materials or workmanship, and provide a simple and inexpensive means of rigidly connecting two ofthese units together to ,form the tandem control.

The present invention further provides an inmrovcmcnt in supporting and coupling two rheostats or control units so that they may be operated in unison for joint control, also The volume control tion ofthe drawings which show a preferred embodiment of my invention to acquaint one skilled in the art with the -teachings'of it, and in which:

Figure 1 is a cross sectional yiew through a cpmpletely assembled4 tandem volume contro Figure 2 is a view through Figurell taken along the line 2 2 looking inthe direction of the arrows;

Figure 3 is afragmentary detail view of the resistance element showing` the method of coupling the separate sections of it electrically together;

Figure 4 is a fragmentary section taken along the line 4--4 of Figure 2 looking in the direction of the arrow and showing the details of the contactor; Y y

, Figure 5 is a plan view of the 'contactorg Figure 6 is a cross-sectional view ytaken along the line 6-6 of Figure 5 anddrawn to an enlarged scale; A l

Figure 7 is a plan view of a terminal lug of the unit;

Figure 8 is an end view of the lug shown in Figure` 7; and, 1 A

Figure'9 is a side elevational view partly in section, of a modified form of my invention.

Referring` to the drawings now in more detail.` the volume control comprises two main units 1 and 2 which are bound within cuplike metalli' shells 3 and 4, which shells are placed with their onen ends adjacent and with their axes'coinciding.V

,The shelll comprises a planar portion 5 and side wall 6 proiecting therefrom at substantially right angles to the planar portion 5. This cup is preferably a metallic cup inade of bra ss or other suitable non-magnetic materiah although the specific material used mav be made within the teachings of the invention.

as.l

which is riveted therein preferably by a ring stake which swedges the metal of the bushing in the shell 3. The outward end of the bushout into the serrations4 in the portion 5. to rigidly lock the bushing 6 against rota/tlon ing 6 is threaded at 9, adapting it to receive the mounting nut 10 by which the unitis mounted on the panel 11 with washer 12 interposed between the nut 10 and the panel.

The planar portion of the shell l3 is also provided with a positioning plate 13 which is provided with a rectangular projection 14, Figure 2, containing a perforation 15 through whichan ear of metal 16 of the panel 11 is projected to prevent rotation of the unit around the bushing 6 when the nut 10 is being tightened. vThis positioning plate 13 is held onto the shell 3 by ears 17 which `are bent-up through perforations 18 in the planar portion 5 of the shell.

Within the shell I have placed a gasket 20 which plays against the inside surface of the planar portion adjacent the side wall 6.

, I have also placed an insulator 21 around the inside surface of the side wall 6, the bottom edge of that insulator resting against the gasket 20. Preferably the insulator 21 contains a pluralitv of ears 22 which project outward bevond the free edgel of the si de wall 6 of the shell 3. and serve as mounting ears for attaching the unit 4 to the unit 3.

The unit 4 is similarlv constructed and comprises a metallic cup having planar portion 24 and s ide wall 25. the planar portion 24 containing a serrated opening through which the. 'bushing 26 is proiected and staked` as at 27 to rigidly attach it to the shell member.

The shell 4 is provided with an insulating gasket 28 and with thevside wall insulator 29,

and the latter insulator is provided with ears 30 which register with the ears '22 on the insulator 21.

The ears of the one insulator are connected 'to the ears of the other in any convenient manner as by eyelets 31 which are riveted through the two projecting ears 22 and 30.

The resistance element 40 is disposed within the shell 3 and a similar element 40 is disposed in the shell 4, the lower edges of these elements bearing against the insulating gaskets 20 and 28 respectively and outer surfaces of the elements bearing against the side wall insulators 21 and 29 respectively The resistance units 40 and 40 preferably comprise an insulating strip 42' which is of generally rectangular cross-section and of suiiicient length to accurately fit around the side wallsof the shell inside of the insulator with its opposite ends abutting each other. The edges of the strip 42 are formed to a somewhat oval shape as at 43, and grooves 44 are cut in the extreme end of this rounded portion, those grooves serving as spacers to space the wire 45 on the strip and to rigidly hold it against movement thereon.

Volume controlv resistors of this type are usually of rather high resistance and in order to make the unit sufficiently compact to fit within commercial radio sets and other similar devices, it is necessary to employ a rather fine or small size resistance wire having a rather high lspecific resistance.

Generally vthe wire used for this purpose is a nickel alloy metal and the diameters are frequently as small as two or three thousandths of an inclu By making the grooves 44 sufficiently deep to practically imbed the -wire over the very edge of the strip, and by spacing these grooves properly the small size wire can be uniformly and rigidly Wound on to the element 42 to secure a permanent resistor.

. The rider or contacter which must bear against the wire 45 to establish an electrical connection therewith is shown in detail in 'Figures 5 and 6 and comprises an annular portion containing a projecting contactl ing arm 51 which is formed as an are, as will be seen in Figure 6. Centrally located within the annular ring 50 is a lobe 52 containing a hexagonal opening 53 located at the geometric center of the ring 50. This lobe 52 'also contains rectangular slots 54 which are provided to permit coupling the 'two units of the volume control together in a manner which will hereinafter appear.

If the contacter 5l were made in the usual manner, that'is so that it contained a flat portion in. engagement with the wire of the unit, and upturned edges to permit that {iat portion to ride over the Wires as the contactor is moved to adjustthe volume control, the sharp' or relatively sharp edges at the point at which the metal is broken from the fiat planar portion to the upturned edges would dig into'and injure the fine wires employed in the volume control. This would be particularly so if any irregularity in the diam-- eter of the wires was encountered, as is frequently the case in commercial practice.

To obviate this diliculty I have provided an arcuate member 51 which presents a perfectly smooth contacting surface which can ride over the small wires 45 on the resistor Without dislodging or injuring them in any way.

To further insure that the contacter 50 will not dislodge or injure the turns of the 'winding and to prevent engagement of the contact member with the insulating strip 42 rather than with the wire such as might occur were wire is thereby interposed between the con-- tact member and the surface of the insulat# ing lstrip nearest the contact member which Vassures proper spacing of the contact member from the insulating strip and prevents engagement of this contact member with the strip rather than with the wire. At the' same time, engagement of the contact member with the wire where it emerges from the grooves places the contacting engagement between the contact member and the wire where the wire is held against displacement on the insulating strip by the movement of the contact member. In the particular embodiment illustrated, the contacting 'member 51 is formed so thatit bears against the wire on the strip 42 at an angle of approximately 65 degrees to the side of the strip 42, but this may, of course. vary widely.

The slot can therefore be made deep enough to practically embrace half of the wire without danger of the contactor 51 riding over the insulation rather than over the wire 45. The bearing point of the contactor 51 pn the wire is sulliciently close-to the slot so that the wire is not moved longitudinally of the inl sulator 42 as the volume control is adjusted.

In these-high resistance resistors used in volume controls and similar apparatus, it is frequently advantageous to form the resistance unit of more than one kind of wire. This is particularly advantageous if a non-uni- .form variation of resistance is required as the rolume control is moved in arcuate path responsiveio a turning of its control knob. To this end various arrangements have been tried heretofore, some employing different size wires-of the same ymateuial, and others employing wires of the same size but of diferont specific resistance. v

In either event, because of the smallness of the wire, that is a wire having a diameter of two or three thousandths of a inch, it is ditlicult to establish a good electrical connec tion between the varioussections forming the resistor. To form such a connection I have provided a method which threads the end of the wire of one section under the first few vturns of the adjacent section and also threads the end of the wire of the adjacent section under the last few turns of the first section.

When the resistor is gripped in the shell of the unit, the overlapping wires are pressed tightly together with sulicient force to insure a good electrical contact.

In carrying'outthis' method, I employ a b'odkin 60 whi'h is threaded under the last few turns 61 of one winding of the resistor.

The end 62 of the wire of the adjacent winding 63 is threaded through the eyelet 64 in the bodkin which is then pulled to thread the wire 62 under the turns 61 where it is disposed substantially at right angles to the wire in those turns.' In Figure 3 this operation is illustrated, the bodkin being shown in the position it assumed prior to pulling the wire 62 under the wires 61 and the wire 62 be- .ing shown dotted in the position it occupies after the bodkin has been removed.v The free end of the'wire 62 is then cut off flush y lwith the surface of the wires 6l andthe process repeated to pull theJ end of the wires 61 under the first few turns of the wire 63 to complte the joint. lVhen the unit is compressed with the wires 61 and 63 firmly held against the insulator 42, the end 62 and corresponding end of the wire 61 is firmly held against its companion wire .to insure a good electrical contact This method otv lacing the end of the wire back under the last few. turns of thewinding is also employed at the eXtreme end of the resistor togprevent the winding thereon from unraveling when the unit is handled during assembly.

To establish electrical connection with the resistor, I have provided contacts 70 which are provided with perforations 7-1 or other suitably shaped ends to which the wires of the external circuit may be attached. The terminal 70 is also provided with serrated edges 72 which are offset slightly to form the lower end of the terminal 70 into a planar portion as shown at 73 in Figure 8. The seri-ations 72 are bent outward away from the central portion of the terminal and when the terminal is assembled in the volume control unit between the resistor 40 and the insulator f 21. Figure 2. the serrations point outward and imbed themselves in the insulator 21.

, One of these terminals 70 is disposed at each end of the winding`45 on the resistor unit, and held therein in the following manner.

The resistor 40, insulator 21 and terminals 70 are placed in the shell 6 on the gasket 20, with the ends of the resistor abutting. The

shell is then shrunk by passing a die down i strength, and this pressure alone is sufficient to prevent the resistor from being pulled out vof the shell.

tended through the hole that `has just been pierced in the shell. The base portion of the terminal 74 overlaps the' terminals 70 Dand thereby assists in keeping those terminals tightly in place. A

The unit 4 is, of course, iinished in a slmilar manner.

The contactor of the unit 3 is fitted 0n to a shaft 80 whichfis disposed within the bushing 6 and which projects from the threaded end of thatbushing to receive a.

knob, not shown, by means of which the contactor is turned to adjust the volume control. The contacter 51 of this spring bears against the resistor 40 and it will be noted that the vextreme end of this arm`51 falls inside of the projecting ear 22 of the insulator`21 so that the contacterV may be turned around without striking those ears. v

Similarly the contacter 50 of the rearward unit 4 is mounted upon a stud shaft 81 disposed wit-hin the bushing 26 Aof the rear iunit, and the contacting arm 51 of thisspring like. wise rides over the element 40 without striking the ears 30 of the insulator 29.

To drive the two units by the operation of a single knob, I have provided an insulating coupling 82. The coupling 82 is in the form kof a thin, Hat plate of insulation notched at its opposite ends to form a pair ofears 83 at each end ot the plate. The ears 83 may be rounded at their free ends as shown, and

these ears extend into the diametricallyI disposed arallel sided slots 54 formed in the lobe o the contact member 50. One ofthe slots 54 is at the free `end of the lobe` 52 opening at one edge therefrom, and the other slot is disposed in theconnecting stock-between the base of the lobe 54 and the surrounding` ring portion of thecontact member and is completely enclosed by the surrounding edge of the contact member. The contact member 50, like the coupling plate 82, is thin so that upon engagement of the ears 83 in the slots 82 and 50 permits relatively great universalA fgeedom therebetween. Great relative tilting movement between the members 82 and 50 is permitted, and the thin edged coopera tion therebetween permits' this relatively great tilting with very slight and almost im-v perceptible clearance between the ears 83 and the thin edges of the slots 5 4.y The engagement of one of the ears 83 in the closedslot call in the connectin stock between the base of the lobe 54 and te surrounding ring portion of the contact holds the coupling plate 82 inlplace against edgewise motionA diametriof the shaft.

o limit the rotary movement of the conprojecting out of the central terminal 74, which ears are disposed adjacent the terminal of the resistor and in the path of the contactor 51 as it rides over the resistor. The ears 84 serve as stops to limit the rota= tion of the 'contactors The electrical circuit through the unit 3 of the volume control may include a complete circuit from terminal 70 through the resistor 40 through the other terminal 70 with the rider arm 51 connected through the bushing 6 and theshell 5`and the rivet 76 to the central contact 73 from which the external circuit may extend. If. the unit is mounted on tactors 50, I have provided upturn ears 84 a metallic panel 11 and-no insulation is' used between the shell and the panel, the rider 51 of the unit 3 will be connectedto the panel which in turn may be grounded. The unit 4 isl similarly connected but since the shell 25 of the unit is electricallyins'ulated from the panel, this unit may be completely electrically insulated from ground and onnected into the electrical circuit at the most opportune point. y A A In Figure 9, I have shown a slightly modiied form of my invention, which form may perhaps be termed the preferred form of the invention.

In thismodification of the invention, the

posed next to the wall 86 of the flange is a narrow strip of insulating material whose width is less than the height of the iange.- I rIhe insulator 102 fits inside of this insulator l 103 and between it and the resistor 87.` The insulator 102 is a wide insulator whose width is approximately twice the height of the flange '86 of the shell100.

In the unit 101,'a wide insulator 105 is disposed next to the flange 88 and a narrow in` sulator 104 disposed within it and, between the insulator 105 andthe resistor unit 89.

When the units 100 and 101 are litted together in the manner shown in Figure 9, the

lwide insulator-.105 of the unit 101' fits on the outside of the wide insulator 102 of the unit 100, the insulator, 105 fitting into an. angular ocket/formed between the outside of the insulator 102 and the inside of the flange 86 of the unit 100. Similarly the wide insulator 102 fits into an angularpocket formed inside of the'wide insulator 105 of the unit 101 and outside of the resistor 89 of that unit.

The insulator 105 is provided with a plurality of circular openings 90 which are so spaced as to lie approximately midway between the two'units when these two units are assembled together in the manner shown in Figure 9. j

To hold the units 100 and 101 in this position, I place a droppf suitable cement or cementitious material in the hole 90, that material adhering to the outside surface of the inner insulator 102 and to the periphery of the opening 90, and forms a seal for rigidly holding the two units 100 and 101 together. The contactors, not shown, of these units are joined together by a coupling meinber such as is shown'at 82 in lfigure 1.-

This improved telescopic cylinder construction shown in Figure 9 produces a rigid volume controL unit oi' greater mechanical strength than is possible with the projecting ears shown in Figure l, and also the workA ing parts and resistors are practically completely encased and therefore protected from injury and from dust by the telescopic cylin-.. drical insulators 104 and 102. The terinistresses without being crushed out of shape,

and since its working parts are adequately protected from the entrance of grit and dirt, the life of the unit is consequently long.

The unit 100 may be provided with a mounting guide plate such as the plate 13 in Figure 1, which has been omitted from Figure 9 as unnecessary. The volume control comprising units 100 and 101 is mounted in the hereinbefore explained manner and opl erated by a single dial or knob attached to the l shaft 93.

. While I have chosen to showl my invention by illustrating a preferred embodiment of it, I have done so by way of example only and am not to be limited bythe disclosure as I am aware there are many modifications and adaptations which can be made by one skilled in the art without departing from the teachings of the invention. j

Having thus complied with the statutes l and shown and described a preferred embodiment of my invention, what I consider new and desire to have protected by Letters Pat-Y tent is pointed out in the appendedclaiins.

1. The method-of assembling a resistance unit in a cup-like shellwhich includes the following operations, lining the shell with insulation, placing a resistance strip within the shell against the insulation, inserting terminals between the strip and insulation, and

shrinking the shell to bind the strip termi- I nals and insulation in place in it.

2. In a rheost'at of the wire wound high resistance type, a strip of insulation having generally rectangular cross section with transverse grooves in its edges which are Aalso' slightly rounded, a. resist ance wire wound on said strip and laid in said grooves to prevent its slipping on the strip, and a contact arm engaging said wire at points where it emerges from said grooves. 3. 1n a rheostat of the wire wound high resistance type, a-strip of insulation having v generally rectangular cross section with transverse grooves in its edges which are also slightly rounded,l a resistance wire wound on said strip and laid insaid grooves to prevent its slipping on the strip, and a movable contact arm having an arcuate member engaging said wire -where itheinergesfrom said grooves and at an angie to the face of said strip. f

4. In a rlieostatzof the wire wound highvresistance type, a strip of insulation having generally rectangular cross section with transverse grooves in its edges which are also slightly rounded, a resistance wire wound on said strip and laid' in said grooves to prevent its .slipping on the strip, and a contact arm having an arcuate member engaging said wire where it emerges from said grooves and teiisioned to bear against the wirefat an angle to the face of the strip. j

5. ln a tandem resistance unit, a pair of cup-like shelisLeach having a resistance element disposed within it, an insulating strip disposed between the walls of each of lsaid cups and said elements, ears'onsaid strips projecting outward from the cup with the ears of one strip registering with the ears of the other and rivets projected through said ears to hold said cups together.

6.- In a tandem ,resistance unit, a pair of cup-like'shells each having a resistance element disposed within it, relatively thin flexible insulation,' means projecting, outward from the open end of one of sa'id shells and registering with a similar means of the other,

. and means for connecting the means of one shell to the means of the other to rigidly fasp ten. the two together. l

7. In a tandem resistance unit, a pair of cup-like shells each having a resistance element disposed within it, a plurality of, eafrsVA projecting outward from the open ends of said-shells with the ears of one shell registering with the earsoof the other, means for connecting the ears of one shell to the ears 'of the othertto rigidly 4fasten the two together, a con acting arm in each shell electrically engaging the resistance element, and an insulating member flexibly connecting l said arms to cause them to be moved synchronously.

8. Ina tandem resistance unit, a pair of cup-like shells each having a resistance element disposed within it, a plurality of ears pro'ecting outward from the open ends of sai shells lwith the ears of one shell registering with the ears of the other, means for connectin the ears of one shell to the ears of thevot er to rigidly fasten the two together, a contacting arm in each shell electrically engaging the resistance element, each of said arms having slots into which the ears of a connecting link fit to connect the arms together for synchronous movement.

9. In a tandem resistance unit, a pair of cup-like shells each having a resistance element disposed within it, a plurality of ears projectin outward from the open ends of said shel s with the ears of one shell registering with the ears of the other, means for connecting the ears of one shell to the ears of the other to rigidly fasten the two together, a slotted contacting arm in each shell electrically en aging the resistance element, and an insulating 1ink,'ears on said link engaging the slots in said arms to connect the arms mechanically lfor synchronous movement.

10. In a tandem rheostat, a pair of cuplike metallic shells each containing a resistance element, insulating strips interposed between said elements and shells, ,said strips extending beyond the open end of the cup and registering with each other, and means for connecting the strips to mount one shell upon the other.

11. In a tandem rheostat, a pair of cup like metallic shells, each containing a resistance element, insulating strips interposed between said elements and shells, said strips extending beyond the o en end of the cup andregistering with eac other, and means including-rivets projected through the projecting edges of said strip for mounting one .shell u on the other.

12. rheostat comprising a metallic cup member, a resistance element wound on a strip and disposed within the cup, insulators between the elementand cup, a pair of terminals disposed between said element and said insulators at the ends of the element, said terminals having serrated edges ybiting intoN said insulators to hold the terminal against lateral and endwise movement, and means for clamping said element, insulators and terminals in sa1d cup.

13. A rheostat comprising ametalic cup member, a resistance element wound on la strip and disposed within the cup, insulators between the element and cup, a pair of terminals disposed Ibetween said. element and said insulators at the ends of the element,

and held against lateral and endwise move t ment, and a terminal includin a plate disposed on the opposite side o the element from said first terminals and riveted through the strip to the cup.

14. A rheostat comprising a `metallic cup member, a resistance element wound 'on a strip and disposed within the cup, insulators between the element and cup, a' pair of terminals disposed between said element and said insulators at the ends of the element, and held against lateral and endwise'movel ment, and means includingian arcuate plate disposed against said element but insulated therefrom and projecting over said termina'ls on the opposite side of the element and riveted through the strip to the cup.

15. lT he combination with a rheostat coming the rheostat and for holding it against 1 turning.

16. In a volume control of the wire wound tandem type, a pair of cup-like shells, a re sistance element in each ofsaid shells, a pair of insulating strips between the elements and shell, the outside strip of the first and the inside strip of the second being narrower thanv said elements and the inside strip of the first and outside strip of the second being wider than said elements, said wide stri s overlapping and secured together to iold the shells in tandem. 1

17. In la volume control of the wire wound tandem type, a pair of cup-like shells, a resistance element in each of said shells, a pair of insulating strips between the elements and shell, the outside strip of the first and the inside strip of the second being narrower than said elements and the inside strip of the first and outside strip of the second being wider than said elements, said wide strips overlapping and secured together with theirfree edges registering with the free edges of said narrow strips to hold the shells in tandem.

18. In combination, a metallic cup-shaped shell having a substantially cylindrical flange and an end wall, a resistance element comprising a wire wound insulating strip of a width slightly in excess of the depth of the flange disposed in said cup and bent into substantially cylindrical shape, a lining of in` sulation interposed between the outer cylindrical side of the element and the flange of the cup and also interposed between the inner edge of the element and theend wall of the cup, and sheet metal terminal members having contacting portions disposed between the element andthe cylindrical part of the lining and contacting with the end turns of no l the winding of the element, the insulating strip of the'element being placed under endwise compression to cause it to be firmly gripped with the fiange of the shell.

19. In combination, a generally cup-shaped ment being placed under end'wise compression to cause it to be firmly gripped with said cup-shaped member and terminal means for the winding of the element.

20. In combination, a pair of electrical circuit controlling devices having operating shafts journaled for rotation, means for mounting said devices with the shafts adjacent to each other and substantially in endwise alignment, a member on one of said shafts, a thin, fiat plate-lil-e coupling member having connection with the other shaft, one of said thin members havin va slot therein and means on the other o said members having engagement in said slot between thin edges of the slottedL member, the engagement of said last means in said slot and with the thin edges of the other member along the slot coupling the shafts together for rotary motion and permitting universal freedom therebetween. f

21. In combination, a pair of rheostats comprising bases which are connected together, circularly .disposed resistance elements mounted on said bases, shafts journaled in said bases substantially in axial alignment, a'thin contact mem er engaging one of the rheostats and mounted on the end of one of the shafts, a thin, flat plate-like insulating coupling member having connection with the other shaft, a thin contact member mounted on said other shaft and engaging the-adjacent rheostat, one, of said thin members having a slot therein, and means on one of the other of said thin membershaving engagement in said slot between thin ed es of the slotted member, the engagement o said l-ast means inl-said slot and with the thin edges of the slotted member along the slot 'couplin the shafts together for rotary motion an permitting universal freedom therebetween. 22. In'coinbinatioma pair of electrical circuit controlling devices'having operating shafts journaled for rotation, means for mounting said devices with the lshafts adjacent to eachother and substantially in endwise'alignment, members on the ends )of said shafts, said thin nembers having diametriv cally disposed narrow parallel sided slots cuit controllingl devices having operatin shafts journaledIv for rotation and restraine against endwise freedom, means for mount-V ing said devices with the shafts adjacent to each other and substantiaily in endwise alignment, thin plate-like members on the ends of said shafts, said' thin .plate-like members havlng diametrically disposed narrow parallel si ed slots with thin edges along said slots, and a coupling member comprisinga thin plate provided with pairs of 'ears at each end,

said ears extending into said slots and cooperable with the thin edges of the plate-like members along said slots for coupling the shafts together for rotary motion and permitting universal freedom, said plate and said plate-like members having interacting shoulders for4 preventing radial displacement of the plate with respect to the slots.

24. In combination, a pair of rheostats having cup-shaped' shells each having a substantially cylindrical fiange and provided with an end wall, a resistance element substantiall circularly disposed within. the flange o each of said shells-and means for mounting said rheostats with the op'en ends of said shells adjacent to each other and substantially in alignment, said last means com` prising insulating strips secured between the resistance elements and the flanges of the respective shells and secured together.

25. In combination, a pair of rheostats having cup-shaped shells each having a substantially -cylindrical flange and provided with an` end wall, a resistance element substantially circularly disposed within-the flange of each of said shells, and meansfor mounting said rheostats with the open ends of said shells adjacent to each other and substantially in alignment, said means comprising thin 'flexible insulating strip means connected together and -secured directly to the respective shells. l

26. In combination, a pair of rheostats hav- -ing cup-.shaped'shells each having a substantially cylindrical flange and providedwith an end wall,'a resistance element substantially circularly disposed within the flange of each'of said shells, and thin flexible insulating strip means'extending between the open ends of said shells an^d at its opposite ends within the flanges of said shells.

27.4 In combination, a. cup-shaped shell having a substantially cylindrical flange open at one end and provided with an end wall at the opposite end, a resistance element comprising a wire wound insulating strip of a width slightly in excess of the depth of the fiai ige disposed in said cup with one edge projecting from the open end thereof, said resistance element being bent into substantiallycylindrical shape with the width of the strip disposed substantially parallel the axis-of the shell, the projecting edge of the strip bein grooved and of generally rounded form an the wire being laid in said grooves to prevent its slipping on the strip and a movable contact member engaging the wire where itA emerges from said grooves whereby substan tially the full thickness of the Wire holds the Contact member out of engagementV with the insulating stri and at the same time displacement of t e Wire by movement lof the contact member is prevented.

28. In combination, a resistance element comprising a Wire Woundl insulating strip bent into substantially cylindrical shape with the Width of the strip disposed substantially parallel to the axis thereof, said strip having an edge which is groovedand of generally rounded form and the wire being laid in said grooves to prevent its slipping on the strip, and a movable contact member engaging the Wire Where it emerges from the grooves whereby the wire holds the contact member out of engagement with the insulating strip and at the same time displacement of the Wire by the movement of the contact member is prevented.

29. In combination, aresistan'ce unit comprising a base, a resistance element mounted on the base, a rlder movably engaging said resistance unit,1a shaft for moving said rider,

a hub for mounting the rider on the shaft, a pair of radial slots in said hub, a second'and similar unit mountedv with its resistance ele-y` ment adjacent the element of the first unit and with its shaft in alignment with the shaft of the irst unit, said second unit being insulated from said first unit, and an H-shaped coupling means engaging the? slots in said hubs and between thin edges along the slots in said hubs and connecting said riders to en able the second to be moved by movement of the first.

In witness whereof, I hereunto subscribe my name this 28th day of December, 1929.

NEWTON o. SCHELLENGER.

CERTIFICATE oF coRREcnoN.

Patent No. 1,833,042., f Granted November 24; 1931, a

" Newtown.v soHELLENGEnV It is hereby certified that error appears in the printed specification`4 of the above numbered patent requiring correction as follows: f Page 7, line 14, claim 20, before the word X'niember'? and line 51, claim 2.2, before the word "members" insert the word thin; end .that'the said Letters .Patent should'be read with these corrections therein that the samel may'conform 'to the record of the lcase in the Patent Office. f

Signed land sealed this 9th day of Febnlary, A. D. 1932-..

M. J.1 Moore,

(Seal) l Act/ini: Connnsanerof Patents. 

